Counterelectromotive force derivation circuit



Aug. 18, 1953 O. E. CARLSON COUNTERELECTROMOTIVE FORCE DERIVATION CIRCUIT Filed April 10, 1953 2 Sheets-Sheet 1 INVENTOR Gscar E. Carlson ATTORNEY Aug. 18, 1953 O. E. CARLSON Filed April 10, 1953 2 Sheets-Sheet 2 "Pic-3.2.

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INVENTOR Oscar E.Car1son Patented Aug. 18, 1953 I OFFICE GOUNTERELECTROMOTIVE FORCE DERIVATION CIRCUIT Oscar E. Carlson, Paterson, N. J.

Application April 10,v 1953, Serial No. 348,081

10 Claims. 1

This invention relates to circuit arrangements for use in connection with electronic speed control systems for direct current motors running from alternating current sources. More particularly, this invention relates to circuits for use with speed control systems of the so-called half wave type, that is, systems in which a direct current motor is connected to an alternating current source through a half wave rectifier device. It is known practice to use thyratron type tubes for the rectifiers in systems of this type.

This application is a continuation-in-part of my co-pending application Serial No. 291,725, filed June l, 1952, and now abandoned, which shows an embodiment of my invention as applied to a uni-directional control system. The present application adds to the disclosure of the parent case by showing the identical invention applied to a bi-directional control system. In order to provide a bi-directional control system, it is only necessary to connect two of the circuits, such as shown in the above mentioned application, together in back to back relationship.

It is also known that a direct current motor supplied with current by a half wave rectifier from an alternating current source, exhibits a voltage across its armature which is an integrated voltage comprising the applied voltage from the rectifier source and the back or counter E. M. F. of the motor. In many cases, it is desirmotor is supplied with current only during half of each cycle of the alternating current source. During the negative portion of the applied cycle, the rectifier, of course, does not conduct and the motor in effect coasts through this portion of the cycle. During this time, therefore, since no voltage is applied to the armature of the motor, it is in effect acting as a direct current generator with no load.

It is an object of this invention to provide a circuit arrangement which will derive a voltage which is directly proportional to the back E. M. F. of a motor operating under these conditions.

It is a further object of this invention to provide a circuit which may be connected in shunt with the armature of the motor, but which will conduct current only during the negative portions of the applied alternating current voltage, 1. e., when no voltage is being applied to the armature of the motor.

It is also an object of this invention to synchronize the gating of the circuit in shunt with the motor armature with the alternations of the alternating current source.

It is also an object of this invention to provide a circuit which will accomplish the above objects and which may be readily added to a standard half wave motor control circuit with a minimum of complexity and expense.

Other objects will be apparent from the following description read in conjunction with the attached sheets of drawing in which:

Figure 1 shows a uni-directional control system embodying the present invention, and

Figure 2 shows the same invention as applied to a bi-directional control system.

Referring now to the drawing for a complete understanding of this invention, the direct current motor I!) which has a separately excited field winding, not shown, is connected in the plate cathode circuit of a thyratron tube H and both are connected in series with a source of alternating current l2. The circuits for controlling the flow of current in the thyratron I I may take any one of a number of known forms. Since this forms no part of the present invention, the grid control circuit is indicated only schematically as a direct current source l3 superimposed upon an alternatin current source 14.

A second tube I5, shown here as a triode, has its plate and cathode connected to opposite sides of the armature of the motor [9 and a condenser is is connected in series with the cathode lead.

By impressing on the grid of the tube it a voltage sufficient to bias the tube to cut off during periods when the alternating current source 12 is applying a positive voltage to the plate of thyratron H, and applying a positive voltage to the grid of the tube i5 during periods when the alternating current source I2 is supplying a negative voltage to the plate of the thyratron ll, the tube l5 may be made to conduct current only during that portion of the applied alternating current cycle when no voltage is applied to the armature of the motor. In order to synchronize, therefore, the gating of the tube l5 with the frequency of the alternating current source I2, a transformer I! is provided. The secondary of transformer H is connected to the grid of tube 15 while the primary is connected directly across the alternating current source 12. From the foregoing it will be apparent that at times when the alternating current source I2 is supplying a positive voltage to the plate of the thyratron H, the instantaneous polarities indi cated on the drawing adjacent the transformer One use which may be made of the voltage which appears across condenser I6 in this'circuit is use as a speed indicator. A voltmeter H3 is connected in series with the resistor I9 across the condenser it. With the resistor-condenser combination proportioned as above, it is possible to achieve a stable voltage across the condenser l and this voltage will be indicated by the meter E8. The latter, of course, may be easily calibrated to indicate directly the speed of the motor IE3.

The additional source of direct current potential in the plate circuit of tube l5, indicated by battery 29, is optional and for the purpose of providing a so-called suppressed zero scale for the meter 18. When used, zero voltage on the meter may represent an actual speed of rotation of the motor it. Obviously the direct current source 21! would have to have its negative side connected to the anode of the tube l5 so as to oppose normal current flow in the tube until the back E. M. F. of the motor rises to a predetermined level.

It will be obvious to those skilled in the art that while the tube i5 is shown herein as a vacuum triode, it could be any grid controlled electronic valve and could also be a so-called hard triode or transistor. It will also be apparent that there are many known equivalents for the thyratron H which would a workable, if somewhat more limited, control.

While the voltage developed in the cathode circuit of the tube l5 directly proportional to the back E. M. F. of the motor ID is used to furnish an indication of speed in the foregoing description and drawing, it will be further apparent to those skilled in the art that other uses could be made of this voltage. It could, for example, be used as a reference voltage to control the firing time of the thyratron l I.

Referring now to Figure 2 of the attached sheets of drawing, a bi-directional control system is shown, The armature 30 of the direct current motor is connected in series with a pair of sources of alternating current voltage 3! and 52 to form, together with thyratrons 33 and 34, a

pair of series circuits which will pass current through the armature in opposite directions. By controlling the grid voltages of the two thyratrons one or the other may be caused to conduct to pass current through the armature in either desired direction for the desired direction of rotation.

It will be understood that the alternating current sources 38 and 32, which are shown diagram matically in the drawing, will in general be a pair of secondary windings of a transformer, the primary winding of which is connected to a single phase alternating current source. For convenience, and to simplify the drawing, they have been shown diagrammatically as have the other sources of current necessary to operate this circuit. In this way, it is also easier to indicate the relative phase relations between the various sources.

In order to apply the invention to a bi-directional control system such as shown, it is necessary to use a pair of triode tubes such as the tube !5 shown in Figure 1. Obviously the two triodes may be contained within the same envelope as shown at in Figure 2. They are inversely connected across the armature of the motor order that one may be made to respond to the back E. M. F. of the motor for one direction of rotation and the other for the opposite direction of rotation. It will be obvious that when one is conducting, the other is out off due to the different polarity of back E. M. F. for different directions of rotation of the motor.

The two sources of alternating current 35 and 37, shown in the grid circuit of tube must bear the same phase'relation to the sources 33 and 3?; as does the grid voltage of tube 55 to the plate voltage of tube l 5 shown in Figure 1. These relations have been schematically indicated on the drawing. Thus, source 36 must be 189 out of phase with source 3! and source 3'5 must be out of phase with source 32. This will insure that the two triode sections will conduct current only when voltage is not being applied to the armature of the motor from the controlling thyratron.

It is possible in this circuit to use a single meter for indicating the back M. F. voltage, providing the meter is of the type having a zero center scale, because it will read in dii'ferent directions for the different directions of rotation of the motor armature. Such a meter is indicated at M in Figure 2. A reactive component the equivalent of condenser it in course, be provided and in this case is shown as condensers 38 and 39 which are connected. in series between the triodes and the motor armature.

to maintain a fairly constant value of voltage appearing across these circuit elements. These elements have the identical function to that described for condenser i6 and resistor is of Figure 1. Resistors d8, t9, and 553 connected across the armature of the motor, together with their ad justable members 5i and 52, serve merely a balancing arrangement.

The sources of voltage 40 and 4| shown in the grid circuits of the thyratrons correspond to source l4 shown in Figure 1 and bear the indicated phase relationship with the plate voltage of the thyratrons. Terminals 42 and 43 provide for connection with a direct current control voltage which will determine the direction of rotation of the motor by permitting conduction in one thyratron and preventing conduction in the other. rection of rotation by rapid reversal of the polarity of the voltage applied to these terminals may readily be accomplished without overloading the circuit components through use of the pair of diodes 44 and 45, and their associated resistors 53, 54, 55, and '56. The battery 51 serves merely as a hold-off bias for the thyratrons 33 and 34. Use of the diodes M and 45 and their associated circuits, however, forms no part of the present invention and is adequately described and claimed in my copending application Serial No. 337,999, filed February 20, 1953, for Bi- Directional Electronic Motor Speed Control.

The following claims are directed to the novelty of the invention described herein, but variations within the scope of the claims will be apparent to those skilled in the art.

Figure 1 must, of,

Resistors it and 3? function together with condensers 3S and 39 to provide a filtering actionv Rapid reversal of the di-.

I claim:

1. In combination with a running speed motor control system, of the type in which a direct current motor is connected to an alternating current source through a half Wave rectifier, a circuit arrangement for deriving a voltage directly proportional to the back E. M. F. of the motor comprising: an electronic valve having an anode, cathode and grid; means connecting the anode and cathode of said valve to opposite sides of the armature of said motor, the anode being connected to the positive side of the armature; a smoothing filter circuit connected in series between said valve and said armature; means connected in the grid circuit of said valve for biasing said valve to cut off during periods when current is being supplied to the armature of said motor from said alternating current source and for initiating current conduction in said valve during that portion of the cycle of the alternating current source when current is not being supplied to said motor; and means for connecting said system and circuit arrangement to a source of alternating current; whereby a voltage is maintained across said smoothing filter circuit which is directly proportional to the back E. M. F. of said motor.

2. A circuit arrangement as defined by claim 1 in which a transformer having its primary winding connected across the alternating current source and its secondary winding connected between the grid and cathode of said valve, is used to initiate and stop current conduction through the valve in the manner set forth in claim 1.

3. In combination with a running speed motor control system, of the type in which a direct current motor is connected to an alternating current source through a half wave rectifier, means for deriving a voltage directly proportional to the back E. M. F. of the motor comprising: an electronic valve having an anode, cathode, and grid; means including a resistive load connecting the anode and cathode of said valve to opposite sides of the armature of said motor, the anode being connected to the positive side of the armature; a transformer having at least a primary and secondary winding; means connecting the primary winding of said transformer to the alternating current source; means connecting the secondary winding of said transformer to the cathode and grid of said electronic valve so phased that whenever the rectifier is conducting current, the grid of the valve is negative; a condenser connected across said resistive load; a voltmeter connected in series with said resistive load; and means for connecting said circuit and voltage deriving means to a source of alternating current; whereby said meter will continuously indicate a voltage directly proportional to the back E. M. F. of the motor.

4. In combination with a direct current motor connected to a source of alternating current through a half wave rectifier, means for indicating the speed of the motor comprising: an electronic valve having an anode, cathode, and grid; means connecting the anode and cathode of said valve to opposite sides of the armature of said motor, the anode being connected to the positive side of the armature; a condenser connected in series with said cathode and said motor armature; a transformer; means connecting the primary winding of said transformer across the alternating current source; means connecting the secondary winding of the transformer between the grid and cathode of said valve in such phase 6 relation that the voltage due to said transformer which appears on said grid is 180' out of phase with the voltage on that side of the rectifier supplying current to the motor which is positive during current flow therethrough; and speed calibrated indicating means connected across said condenser to continuously indicate the speed of rotation of said motor.

5. An electronic motor control circuit comprising in combination: a source of alternating current; a direct current motor; a thyratron rectifier; means connecting said motor to said source through said thyratron rectifier; means connected in the grid circuit of said thyratron rectifier for controlling the firing time thereof; a triode valve; means connecting the anode and cathode of said triode to opposite sides of said motor armature, the anode being connected to.

the positive side of the armature; a transformer; means. connecting the primary winding of said transformer across said alternating current source; means connecting the secondary wind ing of said transformer between the grid and cathode of said triode in such phase relation that the triode grid voltage is 180 out of phase with the plate voltage of said thyratron; a condenser which appears across said condenser during half of each cycle of the alternating current source is maintained substantially constant through the succeeding half cycle.

6. A circuit arrangement as defined by claim 1 and including a source of direct current connected between the anode of said valve and said motor with a polarity opposing that of the motor.

'7. Speed indicating means as defined by claim 4 and including a source of direct current connected in series between the anode of said valve and the positive side of the armature of said motor, the negative side of said source being connected to the anode of said valve.

8. In combination with a running speed motor control system of the type in which a direct current motor is connectable to an alternating current source selectively through one of a pair of oppositely connected thyratrons so that one controls the motor for rotation in one direction and the other for the other direction of rotation, a circuit arrangement for deriving a voltage directly proportional to the back E. M. F. of the motor comprising: a pair of electronic valves each having an anode, cathode and grid; means connecting the anode and cathode of one valve to opposite sides of the motor armature; means connecting the anode and cathode of the other valve to the cathode and anode, respectively, of the first valve; at least one smoothing filter circuit connected in series between said valves and said armature; means connected in the grid circuit of one of said valves for biasing one of said valves to cut off during periods when current is being supplied to the motor armature from one of said thyratrons; means connected in the grid circuit of the other of said valves for biasing the valve to out on" when current is being supplied to the motor armature from the other of said thyratrons; means connected in the grid circuit of one of said valves for initiating current conduction in one of said valves when the motor is connected to the alternating current source through one of said thyratrons and current is not being supplied to the motor armature from said thyranected to the alternating current source through the other of said thyratrons and only when current is not being supplied to the armature of t motor from said thyratron; whereby a voltage is maintained across said smoothing filter circuit which is directly proportional to the back E. M. F' of the motor regardless of the direction of rotation thereof.

9. In combination with a running speed motor control system of the type in which a direct current motor is connectable to an alternating current source selectively through one of a pair of oppositely connected thyratrons so that one controls the motor for rotation in one direction and the other for the other direction of rotation, a circuit arrangement for deriving a voltage directly proportional to the back E. M. F. of the motor comprising: a pair of electronic valves each having an anode, cathode and grid; means connected in the grid circuit of one of said valves for biasing said valve to out off when the motor is connected to the alternating current source through one of said thyratrons and current is being supplied to the armature of the motor through said thyratron, and for initiating current fiow in said valve only when current is not being supplied to the armature of the motor from said thyratron; means connected in the grid circuit of the other of said valves for biasing said valve to cut off when the motor is connected to the alternating current source through the other of said thyratrons and current is being supplied to the armature of the motor from said thyratron, and for initiating current conduction in said valve only when current is not being supplied to the armature of said motor from said thyratron; means including a smoothing filter circuit connected in series between the anode and cathode of one of said valves and the armature of said motor; and means including a second smoothing filter circuit connected in series between the anode and cathode of the other of said valves and the armature of said motor; whereby a voltage directly proportional to the back E. M. F. of the motor is maintained across one of said smoothing filter circuits regardless of the direction of rotation of the motor.

10. A circuit arrangement as defined by claim 9 in which speed calibrated indicating means are connected in circuit with the smoothing filter circuits to continuously indicate the speed of rotation of the motor.

OSCAR E. CARLSON.

References Cited in the file of this patent UNITED STATES PA'I'ENTS Number Name Date 1,944,756 Quarles Jan. 23, 1934 2,573,849 Knauth Nov. 6, 1951 

